Fix FileNotFoundException when reading dependencies

Robolectric throws an exception when `robolectric.offline=true` and `robolectric.dependency.dir` contains spaces.
Dependency path become wrapped into a `URL` in `org.robolectric.LocalDependencyResolver#fileToUrl` and then unwrapped back with `URL#getFile` which returns %20 instead of spaces.

Related stackoverflow question: http://stackoverflow.com/questions/6164448/convert-url-to-normal-windows-filename-java

Stacktrace:

```
java.lang.RuntimeException: java.lang.RuntimeException: java.io.FileNotFoundException: /Applications/Android%20Studio.app/system/Preview/deps/android-all-4.3_r2-robolectric-0.jar (No such file or directory)
	at org.robolectric.RobolectricTestRunner$2.evaluate(RobolectricTestRunner.java:281)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
	at org.robolectric.RobolectricTestRunner$1.evaluate(RobolectricTestRunner.java:196)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
	at org.junit.runners.Suite.runChild(Suite.java:127)
	at org.junit.runners.Suite.runChild(Suite.java:26)
	at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
	at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:160)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:138)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:117)
	at org.junit.runner.JUnitCore.runMain(JUnitCore.java:96)
	at org.junit.runner.JUnitCore.runMainAndExit(JUnitCore.java:47)
	at org.junit.runner.JUnitCore.main(JUnitCore.java:40)
	at com.jetbrains.robowrapper.Robowrapper.main(Robowrapper.java:9)
Caused by: java.lang.RuntimeException: java.io.FileNotFoundException: /Applications/Android%20Studio.app/system/Preview/deps/android-all-4.3_r2-robolectric-0.jar (No such file or directory)
	at org.robolectric.res.Fs$JarFs.<init>(Fs.java:62)
	at org.robolectric.res.Fs.fromJar(Fs.java:25)
	at org.robolectric.SdkEnvironment.createSystemResourceLoader(SdkEnvironment.java:30)
	at org.robolectric.SdkEnvironment.getSystemResourceLoader(SdkEnvironment.java:38)
	at org.robolectric.RobolectricTestRunner$2.evaluate(RobolectricTestRunner.java:276)
	... 25 more
Caused by: java.io.FileNotFoundException: /Applications/Android%20Studio.app/system/Preview/deps/android-all-4.3_r2-robolectric-0.jar (No such file or directory)
	at java.util.zip.ZipFile.open(Native Method)
	at java.util.zip.ZipFile.<init>(ZipFile.java:215)
	at java.util.zip.ZipFile.<init>(ZipFile.java:145)
	at java.util.jar.JarFile.<init>(JarFile.java:153)
	at java.util.jar.JarFile.<init>(JarFile.java:117)
	at org.robolectric.res.Fs$JarFs.<init>(Fs.java:60)
	... 29 more
```